This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-073488, filed Mar. 18, 1999; and No. 2000-049891, filed Feb. 25, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an active matrix liquid crystal display device in which each of display pixel electrodes is constituted with a thin-film transistor as a switching element.
Recently, a liquid crystal display device capable of achieving high-function and high-precision representation of pictures despite a high density and a high capacity has been developed. Although there are various types of the liquid crystal display device, the active matrix liquid crystal display device has been most often used, because a cross-talk between adjacent pixels is small, a high contrast image can be obtained, transmissive display can be achieved, a large area representation can be achieved and other reasons.
Generally, the active matrix liquid crystal display device has an array substrate. This array substrate includes pixel electrodes disposed in plural regions in a matrix configuration, sectioned by plural scanning lines and plural signal lines disposed such that they intersect each other. Each of the pixel electrodes is connected to the scanning line and signal line through a thin-film transistor (hereinafter referred to as TFT) functioning as a switching element.
Although the display quality of such a TFT liquid crystal display device is affected by parasitic capacity between the signal lines and pixel electrodes, an influence of this parasitic capacity can be suppressed by forming an auxiliary capacity or disposing shield electrodes fixed to a predetermined potential so as to overlap the pixel electrodes and signal lines through a layer insulating film.
However, because a large auxiliary capacity is needed to suppress an influence of the parasitic capacity, this is the reason for reducing the aperture ratio of the liquid crystal display device. Further, when the shield electrodes are provided, the load capacity of the signal lines is increased so that the driving load of an incorporated circuit is increased.
Thus, for solving the above problems, the inventors of the present invention have proposed a system wherein a light-sealing layer is formed by the signal lines and shield electrodes. However, the liquid crystal display device having such a structure contains a new problem that when its display screen is observed obliquely from the right and left, light leaks so that contrast drops.
On the other hand, in a liquid crystal display device of a type in which the pixels are disposed above, each of the pixel electrodes cannot be connected directly to a source electrode. Thus, the pixel electrodes are connected to the source electrodes via through holes formed in organic insulating film, and via pixel connecting electrodes formed at the same time as the signal lines.
In this case, taking into account a forming accuracy of the through holes, each of the pixel connecting electrodes is formed in a size larger than that of the through hole. However, because the pixel connecting electrodes are formed at the same time as the signal lines, a maximum size of the pixel connecting electrode is determined by dot pitch, minimum processing dimension and signal line width. If the dot pitch is small, necessarily, the size of the pixel connecting electrode is decreased and at the same time, the through hole diameter of the organic insulating film is also decreased.
Usually, workability of the through holes is low because the film thickness of the organic insulating film is as thick as 2 to 4 xcexcm. Thus, if the through hole diameter is small, point defect due to through hole forming error may be generated. Although it can be considered to enlarge the through hole diameter of the organic insulating film along the signal lines, in this case, it comes that the aperture ratio drops.
The present invention has been contrived in consideration of the above circumstances, and its object is to provide an active matrix type liquid crystal display device having a high display quality in which an occurrence of display error is reduced.
Another object of the present invention is to provide an active matrix type liquid crystal display device in which the display quality thereof is improved by reducing the image error and which is capable of achieving high quality representation of pictures without reduction of the aperture ratio while preventing a through hole forming error when the pixel electrode is electrically connected to the pixel connecting electrode.
To achieve the above object, according to an aspect of the present invention, there is provided an active matrix type liquid crystal display device comprising: first and second substrates opposing each other with interposing a liquid crystal layer between the first and second substrates,
the first substrate including: an insulating substrate; a plurality of scanning lines arranged substantially in parallel with one another on the insulating substrate; a plurality of signal lines provided on the scanning lines via an insulating film and extending in a direction crossing the scanning lines; a plurality of pixel electrodes each of which is arranged in a region surrounded by the scanning lines and the signal lines and connected to an intersection between the signal line and the scanning line via a switching element, each of the pixel electrodes being formed on a layer above the signal lines such that at least part of the pixel electrode overlaps the signal lines; a plurality of auxiliary capacitance lines formed on a layer below the signal lines, each of the auxiliary capacitance lines being arranged between the two adjacent scanning lines and extending in a direction substantially perpendicular to the signal lines; and a plurality of shield electrodes having electrostatic shielding characteristic and extending from the auxiliary capacitance lines along the signal lines.
Each of the shield electrodes has a first electrode portion arranged to overlap only a side edge portion of one of two adjacent pixel electrodes and a side edge portion on the side of the one pixel electrode of the signal line side edge portions; and a second electrode portion arranged to overlap only a side edge portion of the other pixel electrode and the other side edge portion of the signal line, an overlapping width between the shield electrode and the pixel electrode being larger than an overlapping width between the signal line and the pixel electrode.
Further, according to another aspect of the present invention, there is provided an active matrix type liquid crystal display device comprising: first and second substrates opposing each other with interposing a liquid crystal layer between the first and second substrates,
the first substrate including: an insulating substrate; a plurality of scanning lines arranged substantially in parallel with one another on the insulating substrate; a plurality of signal lines provided on the scanning lines via an insulating film and extending in a direction crossing the scanning lines; a plurality of pixel electrodes each of which is arranged in a region surrounded by the scanning lines and the signal lines and connected to an intersection between the signal line and the scanning line via a switching element, each of the pixel electrodes being formed on a layer above the signal lines such that at least part of the pixel electrode overlaps the signal lines; and a plurality of shield electrodes having electrostatic shielding characteristic and extending from the scanning lines along the signal lines.
Each of the shield electrodes has a first electrode portion arranged to overlap only a side edge portion of one of two adjacent pixel electrodes and a side edge portion on the side of the one pixel electrode of the signal line side edge portions; and a second electrode portion arranged to overlap only a side edge portion of the other pixel electrode and the other side edge portion of the signal line, an overlapping width between the shield electrode and the pixel electrode being larger than an overlapping width between the signal line and the pixel electrode.
In the active matrix type liquid crystal display device having such a structure, each of the shield electrodes having electrostatic shielding characteristic is formed by extending part of the auxiliary capacitance line or scanning line, intersects the signal line within a single pitch of the pixels, and overlaps partially a peripheral portion of an adjacent pixel electrode. Thus, an increase of the load capacity of the signal lines is suppressed while a sufficient electrostatic shielding characteristic is maintained. Consequently, an active matrix type liquid crystal display device having a high aperture ratio can be achieved.
Further, by increasing the overlapping width between the shield electrode provided below the signal lines and the pixel electrode, light leakage in an oblique direction decreases. As a result, reduction of contrast does not occur at the time of observation from the right or left sides. Consequently, an active matrix type liquid crystal display device having an excellent display performance can be achieved.
Further, according to still another aspect of the present invention, there is provided an active matrix type liquid crystal display device comprising: first and second substrates opposing each other with interposing a liquid crystal layer between the first and second substrates,
the first substrate including: an insulating substrate; a plurality of scanning lines arranged substantially in parallel with one another on the insulating substrate; a plurality of signal lines provided on the scanning lines via an insulating film and extending in a direction crossing the scanning lines; a plurality of auxiliary capacitance lines each arranged between the two adjacent scanning lines and extending in a direction substantially perpendicular to the signal lines; a plurality of shield electrodes having electrostatic shielding characteristic and extending from the auxiliary capacitance lines along the signal lines; and a plurality of pixel electrodes each of which is arranged in a region surrounded by the signal lines and the auxiliary capacitance lines and connected to an intersection between the signal line and the scanning line via a switching element, each of the pixel electrodes being arranged such that at least part of the pixel electrode overlaps the signal lines and the auxiliary capacitance lines.
Each of the shield electrodes has first and second electrode portions extending in opposite directions from the auxiliary capacitance line along the signal line. The signal line located between two adjacent pixel electrodes has a first side edge portion overlapping one of the pixel electrodes and a second side edge portion overlapping the other pixel electrode. The first and second electrode portions of each shield electrode overlap only the other pixel electrode and the second side edge portion of the signal line.
An overlapping width between the one pixel electrode and the first side edge portion of the signal line is different from an overlapping width between the other pixel electrode, and the second side edge portion of the signal line and shield electrode.
Further, according to yet still another aspect of the present invention, there is provided an active matrix type liquid crystal display device comprising: first and second substrates opposing each other with interposing a liquid crystal layer between the first and second substrates,
the first substrate including: an insulating substrate; a plurality of scanning lines arranged substantially in parallel with one another on the insulating substrate; a plurality of signal lines provided on the scanning lines via an insulating film and extending in a direction crossing the scanning lines; a plurality of shield electrodes having electrostatic shielding characteristic and extending from the scanning lines along the signal lines; and a plurality of pixel electrodes each of which is arranged in a region surrounded by the signal lines and the scanning lines and connected to an intersection between the signal line and the scanning line via a switching element, each of the pixel electrodes being arranged such that at least part of the pixel electrode overlaps the signal lines and the scanning lines.
Each of the shield electrodes has first and second electrode portions extending in opposite directions from the auxiliary capacitance line along the signal line. The signal line located between two adjacent pixel electrodes has a first side edge portion overlapping one of the pixel electrodes and a second side edge portion overlapping the other pixel electrode. The first and second electrode portions of each shield electrode overlap only the other pixel electrode and the second side edge portion of the signal line.
An overlapping width between the one pixel electrode and the first side edge portion of the signal line is different from an overlapping width between the other pixel electrode, and the second side edge portion of the signal line and shield electrode.
In the liquid crystal display device having such a structure, the shield electrodes having electrostatic shielding characteristic extend in opposite directions from the auxiliary capacitance line or scanning line along the signal line and disposed so as to overlap only a side edge portion of the signal line. Therefore, intervals between the shield electrodes become unnecessary. Further, since the signal line and shield electrode have to overlap each other along only one side, the signal line can be formed in a minimum processing width. Consequently, a high aperture ratio can be achieved while the electrostatic shielding effect is maintained and picture quality defects such as cross-talk and unevenness in luminance can be reduced, so that higher quality representation of picture can be achieved.
Further, since that portion of each signal line which overlaps the auxiliary capacitance line or signal line and shield electrode is cut out so that the width thereof is smaller than the other portions, the end portion beside the auxiliary capacitance line or scanning line of the pixel connecting electrode can be expanded by a corresponding amount and the size of the through hole in the organic insulating film can be increased correspondingly. Consequently, forming error of the through holes can prevented, so that the active matrix type liquid crystal display device having few point defects and a high display quality can be achieved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.